What is Certificate Transparency?

Certificate Transparency
is a project started by Google to provide complete transparency
in the process of issuing SSL certificates, in order to avoid
abuse or prevent damage from a compromised Certificate Authority.

This goal is achieved by creating a publicly verifiable and
available log of all certificates signed by a Certificate
Authority. This allows anyone to get a complete list of all the
certificates and verify that they are indeed valid.

Comodo created a search engine
to allow quick access of this list by anyone. It can search
for domains, subdomains, and it also supports wildcards.